A new span of the San Francisco- Oakland Bay Bridge will open to traffic on Sept. 3, a day after the U.S. Labor Day holiday and 11 years after work began, the Metropolitan Transportation Commission said.

The San Francisco-Oakland Bay Bridge, since 1936 the main artery between San Francisco and the rest of the country, will close tonight as crews ready the $6.4 billion replacement of its earthquake-damaged eastern span.

Engineers spotted “hundreds” of cracks in welds on parts produced for the San Francisco-Oakland Bay Bridge in 2008 and were encouraged to stay quiet rather than delay the $6.4 billion project, according to a California Senate committee report.

The operator of the San Francisco- Oakland Bay Bridge and six other spans in the area is selling $750 million in tax-exempt bonds toward a $9 billion program to strengthen the structures against earthquakes.

In their haste to finish the $6.4 billion eastern span of the San Francisco-Oakland Bay Bridge, California officials ordered engineers to overlook cracked welds and other flaws and to avoid documenting problems, two former workers told a state Senate committee yesterday.